1. Field of the Invention
The present invention relates to a magnetostatic wave device employing a magnetostatic wave material propagating magnetostatic waves and a disturbance wave eliminator employing this magnetostatic wave device, and more particularly, it relates to a magnetostatic wave device eliminating a disturbance wave from an input signal and a disturbance wave eliminator employing this magnetostatic wave device.
2. Description of the Related Art
Various studies have recently been made as to a magnetostatic wave device employing a YIG (yttrium-ion-garnet) film. For example, a straight edge resonator (SER) formed by rectangularly cutting a YIG film for resonating magnetostatic waves between opposite end surfaces or the like is proposed as a magnetostatic wave device applied to a high-frequency filter or the like.
FIG. 18 is a schematic perspective vie showing the structure of the aforementioned straight edge resonator as an exemplary conventional magnetostatic wave device.
As shown in FIG. 18, a dielectric substrate 116 is arranged on a conductor 114, a YIG film 112 is arranged on the dielectric substrate 116, and a GGG (gadolinium-gallium-garnet) substrate 113 is arranged on the YIG film 112. An input electrode 111a and an output electrode 111b are arranged on portions of the dielectric substrate 116 located on both sides of the YIG film 112. The YIG film 112 and the GGG substrate 113 are rectangularly worked for resonating magnetostatic waves between the longitudinal end surfaces (end surfaces parallel to the input electrode 111a and the output electrode 111b) of the YIG film 112 thereby forming a straight edge resonator.
According to the aforementioned structure, the input electrode 111a receiving an input signal generates a high-frequency magnetic field corresponding to this input signal. At this time, a dc magnetic field H is applied in a direction parallel to the input electrode 111a and the output electrode 111b and the high-frequency magnetic field generated from the input electrode 111a induces a magnetostatic wave in the YIG film 112, so that this magnetostatic wave propagates through the YIG film 112 and resonates between the longitudinal end surfaces. The output electrode 111b converts this magnetostatic wave to an electric signal, which in turn is taken out as an output signal. Thus, the magnetostatic wave device shown in FIG. 18 functions as a high-frequency filter passing a prescribed high-frequency signal corresponding to the resonance frequency therethrough.
The aforementioned conventional magnetostatic wave device can provide a miniature resonator of 1.4 mm by 4 mm having a dominant mode formed by the resonance of the magnetostatic wave between the longitudinal end surfaces of the YIG film 112. However, the resonance of the dominant mode interferes with resonance of a mode between end surfaces (end surfaces along a direction perpendicular to the input electrode 111a and the output electrode 111b) of the YIG film 112 opposed in the longitudinal direction to result in double-humped resonance.
A magnetostatic wave device formed by coupling two straight edge resonators with each other for increasing the pass bandwidth of the aforementioned conventional magnetostatic wave device is also proposed. FIG. 19 is a schematic perspective view showing the structure of another conventional magnetostatic wave device formed by coupling two straight edge resonators with each other.
The magnetostatic wave device shown in FIG. 19 comprises two YIG films 112a and 112b arranged between a GGG substrate 113 and a dielectric substrate 116 so that the inner opposite end surfaces of the two YIG films 112a and 112b are parallel to each other through a space S. In this magnetostatic wave device, the two YIG films 112a and 112b functioning as straight edge resonators respectively are coupled with each other, and the strength of this coupling is changed by varying the space S between the YIG films 112a and 112b. 
FIG. 20 shows the frequency characteristics of the conventional magnetostatic wave device shown in FIG. 19. When the space S is not more than about 1 mm, for example, the insertion loss is about 15 dB, the 3 dB bandwidth is about 10 MHz and the degree of suppression is about 25 dB, as shown in FIG. 20. Thus, the pass bandwidth can be increased beyond that of the magnetostatic wave device shown in FIG. 18.
Employment of a magnetostatic wave device for eliminating a narrowband disturbance wave superposed on a spectrally diffused input signal of the 2.4 GHz is recently proposed in relation to a spread spectrum communication system employed for a radio LAN (local area network) or the like. In this case, the magnetostatic wave device requires a broad bandwidth of at least about 30 MHz as the 3 dB bandwidth. Therefore, a YIG single-crystalline thin film filtering an input signal in all propagable bands for magnetostatic waves with no frequency selectivity is employed for the magnetostatic wave device. In this case, the pass bandwidth is about 900 MHz, and the insertion loss is about 10 dB.
However, the pass bandwidth of the conventional magnetostatic wave device having the 3 dB bandwidth of about 10 MHz is too narrow for serving as the magnetostatic wave device employed for the radio LAN or the like, although the pass bandwidth can be spread as compared with the conventional magnetostatic wave device shown in FIG. 18. Further, the insertion loss of about 15 dB is too large. Also in this point, the conventional magnetostatic wave device shown in FIG. 19 cannot be applied to the radio LAN or the like.
In the aforementioned conventional magnetostatic wave device employed for the radio LAN or the like, the frequency characteristics of the pass bandwidth are so inferior in flatness that the same may exert bad influence on demodulation of an output signal after filtering, although the pass bandwidth is sufficient.
While the insertion loss of the conventional magnetostatic wave device shown in FIG. 19 can be improved to some extent by reducing the space S, the degree of suppression is so reduced in this case that the magnetostatic wave device cannot pass only a desired high-frequency signal. When the space S is increased to the contrary, the insertion loss is so increased that the magnetostatic wave device cannot pass the desired high-frequency signal without loss although the degree of suppression can be improved to some extent.
A magnetostatic wave device applied to a disturbance wave eliminator is now described.
FIG. 21 is a perspective view showing the structure of still another conventional magnetostatic wave device. In this conventional magnetostatic wave device, a YIG (yttrium-iron-garnet) film 100 is formed on a GGG (gadolinium-gallium-garnet) substrate 200 while an input antenna electrode 300 and an output antenna electrode 400 are formed on the YIG film 100, as shown in FIG. 21.
The operation principle of the magnetostatic wave device is now described. When a dc magnetic field H is applied to the YIG film 100 with constant strength, the directions of magnetic dipoles of electrons are oriented toward the magnetic field H. When a high-frequency magnetic field is locally applied in this case, magnetic dipoles around the high-frequency magnetic field cause precession. This precession of the magnetic dipoles is transmitted to adjacent magnetic dipoles due to interaction between the magnetic dipoles, to successively propagate through the YIG film 100. This wave, having a slow speed and dominant magnetic energy, is referred to as a magnetostatic wave.
In the conventional magnetostatic wave device shown in FIG. 21, a high-frequency magnetic field generated from the input antenna electrode 300 induces a magnetostatic surface wave in the YIG film 100 through the aforementioned operation principle, and this magnetostatic surface wave propagates between the input antenna electrode 300 and the output antenna electrode 400. The output antenna electrode 400 converts the propagating magnetostatic wave to an electric signal and takes out the same.
At this time, a signal input in the input antenna electrode 300 is passed when the signal level is lower than the saturation level of the magnetostatic wave device on a frequency axis, while a signal exceeding the saturation level is limited to an output saturation level and taken out from the output antenna electrode 400. Through such properties, the magnetostatic wave device shown in FIG. 21 is applied to a disturbance wave eliminator as a magnetostatic wave filter.
FIG. 22 is a block diagram showing the structure of a conventional disturbance wave eliminator employing the magnetostatic wave device shown in FIG. 21.
The disturbance wave eliminator shown in FIG. 22 comprises an antenna 101, an amplifier 102, a magnetostatic wave filter 103, a back diffuser 104 and a demodulator 105. The magnetostatic wave device shown in FIG. 21 is employed for the magnetostatic wave filter 103.
The antenna 101 receives a diffusion signal spectrally diffused in the direct sequence system and outputs the signal to the amplifier 102. The amplifier 102 amplifies the received diffusion signal to the saturation level of the magnetostatic wave filter 103 and outputs the amplified signal to the magnetostatic wave filter 103. The magnetostatic wave filter 103 attenuates a signal, included in the input signal, exceeding the saturation level to an output saturation level and outputs this signal to the back diffuser 104. The back diffuser 104 back-diffuses the signal limited to the output saturation level by the magnetostatic wave filter 103 and outputs the back-diffused signal to the demodulator 105. The demodulator 105 demodulates the back-diffused signal and outputs the demodulated signal to an output terminal OT.
Operations of the conventional disturbance wave eliminator having the aforementioned structure are now described. FIGS. 23(a) and 23(b) illustrate the spectra of an input signal and an output signal in and from the magnetostatic wave filter 103 shown in FIG. 22, respectively.
The antenna 101 receives a diffusion signal spectrally diffused with a certain specific pseudo-noise code and a disturbance wave mixed into this diffusion signal. The diffusion signal has spectral characteristics diffused over a wide frequency range at a low level, while the disturbance wave has high-level spectral characteristics in a narrow frequency range in the vicinity of the center frequency of the diffusion signal.
FIG. 23(a) shows the spectrum of the diffusion signal output from the amplifier 102. As shown in FIG. 23(a), the amplifier 102 amplifies the diffusion signal to the saturation level of the magnetostatic wave filter 103, and outputs an amplified diffusion signal a1. The amplifier 102 also amplifies the disturbance wave to a disturbance wave b1.
FIG. 23(b) shows the spectrum of the diffusion signal output from the magnetostatic wave filter 103. As shown in FIG. 23(b), the magnetostatic wave filter 103 operates as a band-pass magnetostatic wave filter passing a signal having a frequency within a pass band P1, for passing a signal up to the aforementioned saturation level while attenuating a signal exceeding the saturation level to the output saturation level. Therefore, the diffusion signal a1 passes through the magnetostatic wave filter 103 to form a diffusion signal a2, while the disturbance wave b1 is attenuated to a level equivalent to the level of the diffusion signal a2 to form a disturbance wave b2.
Thereafter the back diffuser 104 multiplies the output signal from the magnetostatic wave filter 103 by a code identical to the pseudo-noise code used on a transmission side for back-diffusing the same so that the diffusion signal forms a high-level signal in the original narrowband. On the contrary, the disturbance wave is spectrally diffused to form a disturbance wave diffused over a wide frequency range at a low level. Finally, the demodulator 105 demodulates the back-diffused signal to the original data according to a prescribed demodulation system, and the output terminal OT outputs the demodulated data.
As hereinabove described, the conventional disturbance wave eliminator applies the dc magnetic field H having constant strength to the magnetostatic wave filter 103 for implementing a prescribed pass band, i.e., the pass band P1 including the frequency range of the diffusion signal a1. When the operating temperature of the magnetostatic wave filter 103 changes due to change of external environment or heat generation in the disturbance wave eliminator itself, however, the pass band of the magnetostatic wave filter 103 drifts due to this temperature change.
FIGS. 24(a) and 24(b) are diagrams for illustrating a drifting state of the pass band caused when the temperature shifts to a higher side in the conventional disturbance wave eliminator shown in FIG. 22.
When the external temperature is increased to increase the operating temperature of the magnetostatic wave filter 103, for example, saturation magnetization of the YIG film 100 changes to change the optimum operating magnetic field. Consequently, the pass band P1 shown in FIGS. 23(a) and 23(b) drifts to a high-frequency side, to become a pass band P2 shown in FIGS. 24(a) and 24(b). When the magnetostatic wave filter 103 filters the diffusion signal a1 in this state, a low-frequency side signal component of the diffusion signal a1 is attenuated to form a diffusion signal a2xe2x80x2, resulting in disappearance of a signal component in a part a, as shown in FIG. 24(b). When the data is demodulated by back-diffusing the diffusion signal a2xe2x80x2 losing a partial signal component, an error occurs to remarkably deteriorate communication quality.
An object of the present invention is to provide a magnetostatic wave device capable of enlarging a pass bandwidth and flattening frequency characteristics in the pass band without increasing insertion loss.
Another object of the present invention is to provide a magnetostatic wave device, capable of enlarging a pass bandwidth and flattening frequency characteristics in the pass band without increasing insertion loss, which can be readily manufactured.
Still another object of the present invention is to provide a magnetostatic wave device capable of improving the degree of suppression without increasing insertion loss.
A further object of the present invention is to provide a magnetostatic wave device and a disturbance wave eliminator capable of correcting drift of a filtering band resulting from temperature change or the like.
A magnetostatic wave device according to an aspect of the present invention comprises a magnetic layer, having first and second end surfaces, made of a magnetostatic wave material, while a magnetostatic wave propagates between the first end surface and the second end surface in the magnetic layer, and the second end surface has a first part having a first interval with respect to the first end surface and a second part having a second interval different from the first interval with respect to the first end surface.
In the magnetostatic wave device according to this aspect of the present invention, the magnetostatic wave is propagated between the first and second end surfaces of the magnetic layer, while the first part of the second end surface has the first interval with respect to the first end surface and the second part has the second interval different from the first interval with respect to the first end surface. In other words, the magnetic layer is provided therein with two intervals, i.e., the first and second intervals, for propagating the magnetostatic wave, for selectively reflecting a magnetostatic wave having a wavelength twice the first interval between the first end surface and the first part of the second end surface and selectively reflecting a magnetostatic wave having a wavelength twice the second interval between the first end surface and the second part of the second end surface.
Therefore, the range of wavelengths of selectively reflectable magnetostatic waves is so enlarged that the pass bandwidth of the magnetostatic wave device can be enlarged without increasing insertion loss. The first and second intervals of the magnetic layer are different from each other not to abruptly change impedance with respect to the magnetostatic wave between the magnetic layer and the space around the same, whereby impedance matching between the magnetic layer and the space around the same is so improved that the frequency characteristics in the pass band can be flattened. Consequently, the pass bandwidth can be enlarged and the frequency characteristics in the pass band can be flattened without increasing insertion loss.
The first part preferably includes a first end surface part arranged in parallel with the first end surface at the first interval, and the second part preferably includes a second end surface part arranged in parallel with the first end surface at the second interval.
In this case, the first end surface part is arranged in parallel with the first end surface at the first interval and the second end surface is arranged in parallel with the first end surface at the second interval, so that the magnetostatic wave device can more selectively reflect the magnetostatic wave between the parallel end surfaces.
The magnetostatic wave device is preferably a resonator resonating the magnetostatic wave between the first and second end surfaces.
In this case, the magnetostatic wave device selectively resonating the magnetostatic wave between the first and second end surfaces can implement a resonator capable of enlarging the pass bandwidth and flattening the frequency characteristics in the pass band without increasing insertion loss.
The magnetic layer preferably includes first and second magnetic layers arranged at a prescribed interval in a direction intersecting with the first and second end surfaces.
In this case, the magnetic layer is formed by the first and second magnetic layers arranged at the prescribed interval and the first and second intervals of each magnetic layer are different from each other not to abruptly change impedance for the magnetostatic wave between the respective magnetic layers and a space therebetween, whereby the impedance matching between the magnetic layers and the space therebetween is so improved that the frequency characteristics in the pass band can be more flattened.
The magnetostatic wave device preferably further comprises an input line arranged on one of the first and second magnetic layers and an output line arranged on the other one of the first and second magnetic layers.
In this case, the input line is arranged on one of the magnetic layers and the output line is arranged on the other magnetic layer so that the input and output lines and the magnetic layers are in close contact with each other and loss between the input and output lines and the magnetic layers can be reduced for further reducing insertion loss.
A magnetostatic wave device according to another aspect of the present invention comprises a magnetic layer, having first and second end surfaces, made of a magnetostatic wave material in which a magnetostatic wave propagates, while the magnetic layer is separated into a plurality of magnetic layers by at least one groove formed between the first and second end surfaces and the groove has a stepwise section having at least one step.
In the magnetostatic wave device according to this aspect of the present invention, the groove formed between the first and second end surfaces separates the magnetic layer into a magnetic layer having the first end surface and an end surface formed by one side surface of the groove and another magnetic layer having the second end surface and an end surface formed by the other side surface of the groove and the groove has the sectional shape having at least one step, whereby at least one of the magnetic layers has different intervals between the end surfaces so that a resonator formed by coupling a plurality of resonators including a resonator resonating a magnetostatic wave between end surfaces having different intervals with each other can be prepared.
Therefore, at least one of the magnetic layers has different intervals for propagating magnetostatic waves, so that the magnetostatic wave device can selectively resonate a plurality of magnetostatic waves having different wavelengths. Consequently, the range of wavelengths of selectively reasonable magnetostatic waves is enlarged so that the pass bandwidth of the magnetostatic wave device can be enlarged without increasing insertion loss.
The groove has the stepwise section, whereby impedance with respect to the magnetostatic wave is not abruptly changed between the magnetic layers and the groove but impedance matching between the magnetic layers and the groove is so improved that the frequency characteristics in the pass band can be flattened.
Further, the aforementioned resonator can be prepared by forming at least one groove, whereby the resonator is easy to manufacture.
Consequently, the pass bandwidth can be enlarged and the frequency characteristics in the pass band can be flattened without increasing insertion loss, and the magnetostatic wave device can be readily manufactured.
The sectional shape of the groove is preferably deepest at the center of the groove and mirror-symmetrical. In this case, the sectional shape of the groove is deepest at the center of the groove and mirror-symmetrical, whereby end surfaces having different intervals with respect to the first and second end surfaces can be readily formed on each magnetic layer, for further enlarging the pass bandwidth and flattening the frequency characteristics in the pass band.
The groove is preferably formed by machining. In this case, the groove can be formed by machining such as grinding or polishing, whereby a substantially rectangular deep groove can be precisely formed on an arbitrary position of the magnetic layer with no influence by the crystallinity of the magnetic layer or the like as compared with chemical etching or ion milling.
A magnetostatic wave device according to still another aspect of the present invention comprises a magnetic layer, made of a magnetostatic wave material in which a magnetostatic wave propagates, receiving a dc magnetic field applied along a prescribed direction and first and second ferromagnetic layers provided on both ends of the magnetic layer in the direction of application of the dc magnetic field.
In the magnetostatic wave device according to this aspect of the present invention, the dc magnetic field is applied to the magnetic layer made of the magnetostatic wave material propagating a magnetostatic wave along the prescribed direction, and the first and second ferromagnetic layers are provided on both ends of the magnetic layer in the direction of application of the dc magnetic field. Therefore, the magnetic bias effect of the first and second ferromagnetic layers homogenizes the dc magnetic field, which in turn more homogeneously magnetizes the magnetic layer. Consequently, the magnetic layer can efficiently propagate a magnetostatic wave of a dominant mode while suppressing propagation of magnetostatic waves of other modes for reducing interference exerted on the dominant mode by other modes, whereby the degree of suppression can be increased without increasing insertion loss.
The first and second ferromagnetic layers are preferably formed on the main surface of the magnetic layer. In this case, the first and second ferromagnetic layers can be brought into close contact with the magnetic layer, whereby the magnetic bias effect of the first and second ferromagnetic layers can efficiently act on the magnetic layer for further improving homogeneity of magnetization in the magnetic layer.
Opposite ends of the first and second ferromagnetic layers are preferably not parallel to each other. In this case, parts of the magnetic layer along the ends of the first and second ferromagnetic layers define reflection interfaces, which are not parallel to each other since the opposite ends of the first and second ferromagnetic layers are not parallel to each other, for reflecting magnetostatic waves of other modes propagating through the magnetic layer to a direction between the first and second ferromagnetic layers. Thus, resonance of the magnetostatic waves of other modes propagating through the magnetic layer can be suppressed to the direction between the first and second ferromagnetic layers, whereby interference exerted on the dominant mode by other modes can be sufficiently reduced for further improving the degree of suppression as well as insertion loss.
The first and second ferromagnetic layers are preferably made of a hard magnetic material. In this case, the quantity of spins not contributing to resonance of the dominant mode in the magnetic layer can be reduced, whereby the magnetic bias effect of the first and second ferromagnetic layers can be more improved for further improving the degree of suppression as well as insertion loss.
The magnetic layer preferably has first and second end surfaces parallel to each other, and the magnetostatic wave device is preferably a resonator resonating a magnetostatic wave between the first and second end surfaces.
In this case, a magnetostatic wave of a dominant mode propagating between the first and second end surfaces can be efficiently resonated between the first and second end surfaces while resonance of magnetostatic waves of other modes can be suppressed for reducing influence exerted on the dominant mode by other modes, whereby a resonator improved in degree of suppression can be implemented without increasing insertion loss.
The magnetic layer preferably includes a plurality of magnetic layers, the plurality of magnetic layers are preferably so arranged that first and second end surfaces of magnetic layers adjacent to each other at a prescribed interval are parallel to each other, and the first and second ferromagnetic layers are preferably provided on each of the plurality of magnetic layers.
In this case, the plurality of magnetic layers can form resonators respectively so that the plurality of resonators can be coupled with each other, whereby the pass bandwidth can be enlarged.
A magnetostatic wave device according to a further aspect of the present invention comprises a magnetic body made of a magnetostatic wave material in which a magnetostatic wave propagates, a dc magnetic field applier applying a dc magnetic field to the magnetic body and an auxiliary magnetic field applier applying an auxiliary magnetic field having adjustable field strength to the magnetic body in addition to the dc magnetic field applied by the dc magnetic field applier.
In the magnetostatic wave device according to this aspect of the present invention, the auxiliary magnetic field applier having adjustable field strength applies the auxiliary magnetic field to the magnetic body in addition to the dc magnetic field applied by the dc magnetic field applier. When saturation magnetization of the magnetic body is changed by temperature change or the like to change the optimum operating magnetic field as well as the filtering band of the magnetostatic wave device, therefore, the auxiliary magnetic field applier can adjust the strength of the auxiliary magnetic field for optimally setting the magnetic field applied to the magnetic body, whereby drift of the filtering band resulting from temperature change or the like can be corrected.
The auxiliary magnetic field applier preferably includes an electromagnet generating a magnetic field by feeding a current to a coil.
In this case, the strength of a magnetic field generated from the electromagnet can be precisely adjusted by applying a current to the coil of the electromagnet and controlling the value of this current, whereby the auxiliary magnetic field can be applied with desired field strength by the simple method of controlling the value of the current fed to the coil, and drift of the filtering band resulting from temperature change or the like can be precisely corrected.
The auxiliary magnetic field applier may include an auxiliary magnetic field application film generating a magnetic field when fed with a current.
In this case, the strength of the magnetic field generated from the auxiliary magnetic field application film can be precisely adjusted by applying a current to the auxiliary magnetic field application film and controlling the value of this current, whereby the strength of the auxiliary magnetic field can be optimally adjusted by the simple method of controlling the value of the current fed to the auxiliary magnetic field application film. Further, the auxiliary magnetic field can be applied by the simple structure employing the auxiliary magnetic field application film, whereby the device can be miniaturized.
The magnetostatic wave device preferably further comprises a substrate having the magnetic body arranged on its main surface, and the auxiliary magnetic field application film and the magnetic body are preferably arranged to hold the substrate therebetween.
In this case, a magnetic body having excellent characteristics as a magnetostatic wave medium can be readily formed on the substrate while the auxiliary magnetic field application film is arranged oppositely to the magnetic body through the substrate, whereby an input antenna electrode and an output antenna electrode can be readily formed on the main surface of the magnetic body with no influence exerted by the auxiliary magnetic field application film. Further, the substrate is held between the auxiliary magnetic field application film and the magnetic body, whereby heat generated by energization of the auxiliary magnetic field application film can be prevented from direct conduction to the magnetic body and influence by heat generation of the auxiliary magnetic field application film can be suppressed.
A disturbance wave eliminator according to a further aspect of the present invention, eliminating a disturbance wave from an input signal, comprises a magnetostatic wave device including a magnetic body made of a magnetostatic wave material in which a magnetostatic wave propagates, a dc magnetic field applier applying a dc magnetic field to the magnetic body and an auxiliary magnetic field applier applying an auxiliary magnetic field having adjustable field strength to the magnetic body in addition to the dc magnetic field applied by the dc magnetic field applier and a control unit controlling the strength of the auxiliary magnetic field generated from the auxiliary magnetic field applier, while the magnetostatic wave device is a magnetostatic wave filter having a prescribed filtering band and the control unit includes a detector detecting change of the filtering band of the magnetostatic wave filter and a current controller controlling the value of a current supplied to the auxiliary magnetic field applier in response to the change of the filtering band detected by the detector.
The disturbance wave eliminator according to this aspect of the present invention detects change of the filtering band of the magnetostatic wave filter and controls the value of the current fed to the auxiliary magnetic field applier in response to the detected change of the filtering band. When the filtering band of the magnetostatic wave filter is changed by temperature change or the like, therefore, the auxiliary magnetic field applier can adjust the strength of the auxiliary magnetic field in response to the change of the filtering band for optimally setting the magnetic field applied to the magnetic body, whereby drift of the filtering band resulting from temperature change or the like can be corrected. Consequently, the filtering band of the magnetostatic wave filter can be regularly set in a proper range, whereby communication quality can be regularly kept excellent.
The detector preferably includes an insertion loss detector detecting change of insertion loss of the magnetostatic wave filter.
When the filtering band of the magnetostatic wave filter changes, the insertion loss also changes in response to the change of the filtering band, and hence the change of the filtering band resulting from temperature change or the like can be detected by detecting the change of the insertion loss.
The insertion loss detector preferably detects change of insertion loss on an edge of the filtering band of the magnetostatic wave filter.
In this case, the insertion loss detector detects change of the insertion loss on the edge remarkably changing the insertion loss when the filtering band changes, whereby the change of the filtering band can be detected with high sensitivity.
The insertion loss detector preferably detects change of insertion loss on high- and low-frequency side edge portions of the filtering band of the magnetostatic wave filter.
In this case, the insertion loss detector detects change of the insertion loss on the high- and low-frequency side edge portions of the filtering band of the magnetostatic wave filter, whereby change of the filtering band can be detected also when ripple or the like is caused on either the high- or low-frequency side of the filtering band, for reliably detecting change of the filtering band.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.